The present invention relates to an electromagnetic relay and a method of adjusting the same and, more particularly, to an electromagnetic relay having such a structure that facilitates adjustment of a contact follow, a method of adjusting the same, and a method of assembling the same.
U.S. Pat. No. 5,894,253 (reference 1) discloses a conventional electromagnetic relay, particularly, a high-breakdown-voltage electromagnetic relay suitable for high-load use for an automobile wiper, power window, or the like.
This electromagnetic relay has a basic structure in which a yoke having a U-shaped section is press-fitted and fixed in a spool wound with a coil. Flange portions are formed on the two ends of the spool, and projections that determine the upper limit of press fitting of the yoke project from the flange portions toward a hollow portion in the spool. Ear-like projections are formed on the two side surfaces of each of the two upright portions of the yoke. The yoke and the flange portions of the spool are positioned by using the two side surfaces of the ear-like projections as the press-fit surfaces that abut against the wall surfaces in the flange portions of the spool, and the two abutting surfaces above the press-fit surfaces.
An armature having a movable contact extends through the hollow portion of the spool, and one end of the armature is connected to one end of the yoke through a hinge spring. Stationary contact terminals formed on the upper and lower surfaces of the movable contact are press-fitted and fixed in the spool. As a result, the number of components is decreased and the assembly process is simplified, thereby reducing the manufacturing cost.
The conventional electromagnetic relay described above is based on a technique having an assumption that the spool and the yoke are mutually positioned precisely. A possibility of variations in contact follow due to the assembly precision or assembly variations is not described at all. The contact follow is a distance through which the armature moves after the making side contact is closed. Factors that cause the variations in contact follow are firstly variations in press-fit position of the yoke and the bending precision of the magnetic pole surface of the yoke, secondly variations in built-in positions of the spool and the terminals, and thirdly the warp of the spring which occurs when caulking the armature and the movable spring.
When the contact follow varies, the service life of the electromagnetic relay becomes unstable. The variations in contact follow cause variations in contact travel, leading to variations in working voltage. Therefore, in order to further stabilize the service life and the working voltage, adjustment of the contact follow during or after assembly is sought for so that the contact follow becomes stable.
Even if the yoke and the spool are assembled with high positioning precision, the contact follow may vary due to various reasons as described above, and final adjustment is accordingly indispensable. In particular, this adjustment need be performed easily and simply, and an arrangement for realizing such an electromagnetic relay, a method of adjusting the same, and a method of assembling the same are sought for.
It is an object of the present invention to provide an electromagnetic relay in which positioning adjustment of a yoke can be facilitated, a method of adjusting the same, and a method of assembling the same.
In order to achieve the above object, according to the present invention, there is provided an electromagnetic relay comprising a spool having a hollow portion and first and second flange portions formed at two ends thereof, a coil wound on the spool, a U-shaped yoke locked at the flange portions of the spool by press fitting to stride over the coil, an armature movably connected to one end of the yoke and positioned to extend through the hollow portion of the spool, a movable contact attached to move in an interlocked manner with the armature, a pair of stationary contacts arranged to sandwich the movable contact, and a first taper portion formed on at least one of press-fit locking surfaces of one end of the yoke and the first flange portion and having a locking force that increases as being closer to a vicinity of the hollow portion of the spool.